a) Field of the Invention
This invention relates to a novel process for synthesis of aromatic sulfides including polysulfides.
b) Description of Prior Art
Diaryl sulfides can be synthesized by several reactions including nucleophilic displacement or aryl halides with aromatic thiols catalyzed by nickel (o) or nickel (I) complexes (Takagi, K. Chem. Lett. 2221 (2987), and Cristau, H. J.; Charaud, B.; Chene, A. H.; Synthesis, 892 (1981)), or with arylthiocuprates (Campbell, J. R. J. Org. Chem. 27, 2207 (1962)), sodium sulfide (Hilgetag, G.; Martini, A., Preparative Organic Chemistry, 4th Ed.; John Wiley & Sons: Toronto, 1972; pp. 636-637) or Grignard reagents (Burton, H.; Davy, W. A. J. Chem. Soc. 528 (1948)); the Friedel Crafts reactions using sulfuryl dihalides or arylsulfenyl halides catalyzed by aluminum or iron have also been used (Wilson, H. F.; Tarbell, D. S. J. Am. Chem. Soc. 72, 5200 (1950)), as has a modified Ziegler reaction utilizing the reaction of diazonium salts and arylthiols (Petrillo, G.; Novi, M.; Garbarino, G.; Dell'Erba, C. Tetrahedron Lett. 26, 6365 (1985)); finally there have been used extrusion reactions of aryl disulfides with phosphines (Harpp, D. N.; Gleason, J. G. J. Am. Chem. Soc. 93, 2437 (1971)) or by heating typically at 250.degree.-300.degree. C. in accordance with Equation 1 below. ##STR1##
Diaromatic sulfides may be employed as precursors or intermediates for a variety of compounds, for example, p-halogenated diaryl sulfides can be oxidized to sulfones which can be reacted with bisphenol A to produce polyethersulfones.
Poly(p-phenylene sulfide) (PPS) is an important high temperature engineering thermoplastic with good mechanical strength, thermal stability, excellent chemical resistance, flame resistance and good electrical characteristics. (Hill and Brady Polym. Eng. Sci. 1976, 16, 832 and Short and Hill Chem. Technol., 1972, 1, 481). The commercial process for the preparation of PPS is based on the method of Edmonds and Hill, U.S. Pat. No. 3,354,129, involving polycondensation of p-dichlorobenzene with sodium sulfide in N-methylpyrrolidone at 240.degree.-260.degree. C. under pressure. PPS has also been synthesized by Lenz (Lenz et al, J. Polym. Sci. 1962, 58, 351) by the self-condensation of p-halobenzenethiolates in pyridine or/and quinoline at high temperatures. Recently copoly(phenylene sulfide-disulfide) containing only very small amounts of disulfide linkages has been synthesized by the direct reaction of sulfur with p-diiodobenzene (U.S. Pat. No. 4,859,762). Other synthetic routes that have been investigated include: 1) the electrophilic substitution of benzene with elemental sulfur in the presence of aluminum chloride (Kreja et al, Angew. Makromol. Chem. 1986, 141, 77); 2) the S.sub.RN 1-type polymerization of p-bromobenzenethiolate initiated by a diazonium salt in DMSO at room temperature (Novi, M.; Petrillo, G.; Sartirana, M. L. Tetrahedron Lett. 1986, 27, 6129), 3) the oxidative polymerization of diphenyl disulfide with antimony pentachloride or quinones or vanadyl acetylacetonate under air atmosphere at room temperature, (Tsuchida, E.; Yamamoto, K.; Nishide, H.; Yoshida, S.; Jikei, M. Macromolecules 1989, 22, 2438 and 1990, 23, 2101; and Tsuchida, E.; Yamamoto, K.; Yoshida, S.; Jikei, M.; Nishide, H. Macromolecules 1990, 23, 930). However, polymers prepared by these methods either contain variable amounts of cyclic and crosslinked species (see Kreja et al above) or they are obtained in very low yields (3.9-28%) (see Novi et al above), or they are low molecular weight (ca. 10.sup.3) and have low melting points (113.degree.-191.degree. C.) (see Tsuchida et al above).